In the smelting of iron ore in a blast furnace alternate charges of coke and ore fluxes are loaded into the top of blast-furnace blast-furnance shaft. Hot air is blown into the base of the bosh of the furnace and passes upwardly through the layered charges, causing part of the coke to burn and form carbon monoxide so as to heat the coke and drive the carbon dioxide out of the limestone fluxes. The upwardly passing hot gas, above 1000.degree.C, dries the ore in the shaft of the furnace and passes out as top gas. A body of molten iron forms in the bottom of the furnace and a layer of slag on top of it, both of the iron and the slag being tapped off at intervals.
It is known to replace part of the metallurgical coke by so-called auxiliary combustibles which are introduced into the furnace by means of air jets at the level of the tuyeres. This use of auxiliary combustibles reduces the need for increasingly expensive and hard-to get metallurgical cokes, the auxiliary combustibles usually being substantially cheaper. Furthermore the auxiliary combustibles frequently make the smelting operation easier to control. As a rule such auxiliary combustibles are liquid or gaseous hydrocarbons--fuel oil or natural gas--as well as town gas.
It is also known to inject coal in a finely divided powder form directly into a blast furnace. Such a method allows relatively cheap coal to be used directly in the smelting operation, but has been found disadvantageous in that the coal must be dried carefully and then ground to a very fine powdery state. This processing of the coal adds considerably to its cost and, therefore, makes such a method as expensive as one using the more expensive coke directly.